Break in period

[was92v]

Do you guys think there is a difference between a new engine /gearbox and rebuilding an engine that all the other hundreds of parts are already run in?
There are hundreds of friction points in a new engine/gearbox that are lapping in besides the cylinder walls, piston skirts and rings in a new motorcycle engine/gearbox that are not at all a concern when rebuilding a used unit. I worry more about gear tooth faces, dog surface and bearing run in, than the ring to wall seal. With the rings and the cylinder finish used these days, unless something was screwed up when it was built, the ring/wall seal in a done deal almost as soon as you start the engine. After rebuilding an engine, a couple of heat cycles to shape the piston is about it. All the rest is already done.

[Tmall]

Originally Posted by was92v

Do you guys think there is a difference between a new engine /gearbox and rebuilding an engine that all the other hundreds of parts are already run in?
There are hundreds of friction points in a new engine/gearbox that are lapping in besides the cylinder walls, piston skirts and rings in a new motorcycle engine/gearbox that are not at all a concern when rebuilding a used unit. I worry more about gear tooth faces, dog surface and bearing run in, than the ring to wall seal. With the rings and the cylinder finish used these days, unless something was screwed up when it was built, the ring/wall seal in a done deal almost as soon as you start the engine. After rebuilding an engine, a couple of heat cycles to shape the piston is about it. All the rest is already done.

Every thing I've touched is honed and within spec from the factory. If it isn't, it goes back. So, I'm not quite sure what you're getting at.


If it's within spec, it will fit. If it's a faulty component, it's going to break regardless of break in. So, what benefit is there to babying it?




I wish I had my "transmission of power" notes kicking around. I can't seem to think of the manufacturing process used in gear design. Burnishing, lapping, hobbing, whatever the heck it is costs a lot and is far more accurate and is commonly used in engine applications.

Ultimately, the only time I've seen catastrophic engine failure has been because of maintainer error.

Edited to add: Most times spun bearings are caused by lack of lubrication. Crank bearings and cam bearing are made out of babbit for a reason, to allow particle embedding to the bearing and not the major components as well as to allow the bearing to wear instead of the expensive parts. And crucial components such as cams usually have bearings matched to them to precise tolerances. The ones we use, if you ding the cam or bearings, you replace everythign as a set. And to do that, we have to send the block away to have new cam bearings pressed in.
These components cost more initially for a reason, they're made to more precise tolerances using more expensive manufacturing processes.

[RedRider2k2]

Originally Posted by was92v

Do you guys think there is a difference between a new engine /gearbox and rebuilding an engine that all the other hundreds of parts are already run in?
There are hundreds of friction points in a new engine/gearbox that are lapping in besides the cylinder walls, piston skirts and rings in a new motorcycle engine/gearbox that are not at all a concern when rebuilding a used unit.

No, not really. All those friction points you speak of are either replaced with new or measured to make sure they're within Spec. You dont toss on a new set of rings and call it "Rebuilt". I'm talking front to back, top to bottom, EVERYTHING gets stripped down and gone over with a micrometer.